Question 1092089
Convert minutes to hrs
{{{ 15/60 = 1/4 }}} hrs
{{{ 10/60 = 1/6 }}} hrs
Let {{{ s }}} = her speed in still water
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Going upsteam:
(1) {{{ d = ( s - 4 )*(1/4) }}} km
Going downstream:
(2) {{{ d = ( s + 4 )*(1/6) }}} km
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{{{ ( s - 4 )*(1/4) = ( s + 4 )*(1/6) }}}
Multiply both sides by {{{ 12 }}}
{{{ 3*( s - 4 ) = 2*( s + 4 ) }}}
{{{ 3s - 12 = 2s + 8 }}}
{{{ s = 20 }}}
The speed in still water is 20 km/hr
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check:
(1) {{{ d = ( 20 - 4 )*(1/4) }}}
(1) {{{ d = 16/4 }}}
(1) {{{ d = 4 }}} km
and
(2) {{{ d = ( 20 + 4 )*(1/6) }}}
(2) {{{ d = 24/6 }}}
(2) {{{ d = 4 }}} km
OK